Carbohydrates have had a history of being demonised, but what are they? This blog is going to cover what they are, and why they shouldn’t be feared.

Carbohydrates are a macronutrient, which means that we eat them in fairly large amounts in our diet (protein and fats are also macronutrients). These macronutrients are involved in energy, growth and repair, and maintenance of the body.

Carbohydrates when eaten are broken down in the body into glucose. Glucose is our main source of energy to keep us functioning, and is used by our muscles, and our major organs. Glucose is even your brain’s preferred and primary energy source! If we do not get enough carbohydrates in our diet, our body will convert fatty acids into a form of energy which can be called upon (known as ketones) to meet the needs of energy requirement for our brain, or certain amino acids (dietary proteins) will be used. For every 1 gram of carbohydrates consumed it provides 4 calories.

Carbohydrates can be separated into the following categories:

  • Simple (Free Sugars) - foods that come into this category are any which have any sugars added to food, such as biscuits, chocolate cakes, jams (with added sugar) and sweets. However, this also includes sugars which are naturally occurring, such as honey, fruit and vegetable juices, purees and syrups
  • Complex (Starchy Carbohydrates) - pastas, rice, bread, potatoes, lentils, oats, and pulses

Note: Some carbohydrates which are deemed complex or starchy, can be refined or processed, (for example, white pasta or bread), whereas others can be less refined, (such as wholegrain pasta, or wholegrain bread)

Simple free sugars are broken down faster than complex carbohydrates, which are broken down slowly. Although fruit, milk, and even some vegetables contain natural sugars they are not counted as free sugars if in their natural form. However, you will find that they are included in the ‘of which sugars’ on food labels. 

Starchy carbohydrates, fruits and vegetables will provide you with energy, as well as vitamins and minerals. They also provide you with fibre, which I’ll discuss the importance of further down.

How much free sugars should I have?

  • For adults (and children aged 11+) it is recommended that we aim to have no more than 30g of free sugar a day (which is around 7 teaspoons). To see how much free sugars is in something it is worth checking the label of the product - be aware of the recommended serving size as this varies product to product (and what you actually eat!)
  • For children aged 7 to 10, they should aim for no more than 24g of free sugar (6 sugar cubes) per day
  • For children aged 4 to 6, they should have no more than 19g of free sugars a day (5 sugar cubes)
  • There is no guideline limit for children under 4years, it is recommended that they avoid food and drinks with sugar added to it

Will carbohydrates make me fat?

If you were eating an excess amount, then yes. However, it is not specifically carbohydrates which do this. All food contains energy, so excess amounts of energy, in relation to energy expenditure will lead to weight gain. The amount of carbohydrates needed per person varies, however, as a general guide a portion is roughly the size of your fist, but this will depend on your needs and your lifestyle.

Why do people lose weight quickly after cutting out carbohydrates?

We are able to store some carbohydrates in our muscles, and our liver. These carbohydrates are stored as glycogen, and any glycogen in the muscles remains here to only fuel the muscle itself (i.e. it isn’t used to fuel other tissues and organs). However, to be stored it needs water. For every 1 gram of glycogen stored, we need at least 3 grams of water. So, in the case where people cut out carbohydrates, they deplete their glycogen stores (as glucose is the preferred energy source), and also lose the water that was stored with the glycogen, which means that fluid is lost and therefore weight! Essentially, it is water weight you are losing and not fat with the initial weight loss seen. You do not need to completely cut out carbohydrates to lose weight.

Carbohydrates also play a role in transporting tryptophan to the brain, which plays an important role in making serotonin our happy hormone!

What is glycaemic index?

Something that people have often heard of is glycaemic index (GI). Carbohydrates are broken down and absorbed at different rates, what GI looks at is which carbohydrates are broken down into glucose quickly (high GI), and which ones are more slowly broken down (low GI). It is useful to know about GI if you need to measure your blood glucose levels, however, a low GI doesn’t always mean something is healthier… a banana has a higher GI, than Nutella due to the fat content slowing the release of sugar from the Nutella.


So, fibre came up earlier, but why is it important? It’s recommended in the UK that we aim to get 30g of fibre per day, but for most of us we do not achieve this, and the average intake for adults is around 18g per day. 

Fibre can be found in bread, beans, lentils, fruits and vegetables. We cannot break down fibre and absorb it for energy, and instead it helps to keep our digestive system healthy, by promoting good gut health. However, it has now been noted that some metabolism and utilisation does occur in the large intestines by our bacteria here which is why the European Commission now considers dietary fibre to have an energy value of 2kcal per gram.

Low fibre intakes are associated with an increase in constipation, diverticulitis, and even risk of bowel cancer. By having a high fibre diet, it can help to reduce cholesterol, reduce the risk of diabetes, as well as helping you to maintain a healthy bowel movement and a healthy gut microbiome by feeding your gut bacteria.

Fibre comes from plant foods which cannot be broken down by our digestive enzymes, however, when it reaches the large intestine it is fermented by our gut bacteria, producing short-chain fatty acids and gas. Fermentable fibre includes fruits, vegetables, nuts and oats. Other fibre which is not fermented adds bulk and helps to reduce transit time, in turn reducing constipation, and includes cereal grains, wheat, rye, barley, and oats.

If you currently consume a small amount of fibre and want to increase it, you should do this slowly to try and reduce the risk of abdominal distention (bloating), and discomfort, and also make sure that you are drinking enough water.

Some food choices for you which are god sources of fibre are porridge, sweet potatoes, potatoes with skin on, wholemeal and wholegrain pastas and breads, beans and pulses, vegetable and fruits (not juiced, or pureed), seeds and nuts. On food labelling anything with more than 6g of fibre per 100g is classified as high in fibre. 

Quality and Quantity

When looking at your carbohydrates it’s important to consider quality and quantity. Try and aim to have a higher intake of your complex/starchy carbohydrates while trying to ensure that you choose the less processed, wholegrain option. However, if you have white rice or pasta from time to time, this is completely fine! Try and go for fruits and vegetables in their whole form instead of having them as juices, as this removes the fibre and increases the rate that the natural sugars are absorbed.

5 a day

In the UK it is recommended that we aim to get 5 portions of fruit and vegetables a day. This is due to the vitamins and minerals they contain, as well as antioxidants, phytonutrients and fibre. For a portion to be counted it needs to be around 80g. You can read more about 5 a day in our blog here


You don’t need to ban or cut out carbohydrates from your diet, they play a role in providing us with energy, fibre, and vitamins and minerals. It’s important to remember to look at the quantity and quality of the carbohydrates you consume, but also enjoy when you have things that aren’t wholegrains or high in fibre from time to time!

If you have a medical condition which impacts the metabolism and utilisation of carbohydrates like Type 1 Diabetes, or Type 2 Diabetes, please follow the advice  given by your doctor, or health care professional.


This blog covers some nutritional science behind carbohydrates and general queries people usually have in relation to them. It covers general guidelines for the general population and it is not specific dietary advice. I am not able to give specific dietary advice over the internet.



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